The present invention relates to an apparatus for friction false twisting an advancing yarn, of the type having a yarn twisting assembly composed of at least three spindles mounted for rotation about parallel axes. More particularly, the present invention relates to a novel mounting structure for the spindles of such an assembly.
Such a friction false twist unit is known, for example, from DE OS 29 36 791. In this known friction false twist unit, the driven shafts, also described as friction element spindles, are supported at their one end with a radial play in a stationary mounting support or bedplate of the friction false twist unit, whereas at their other end they are arranged radially fixed in the bedplate.
Within the radial play, the friction element shaft is flexibly supported and suspended in a certain manner for damped movement.
In the known embodiment this is accomplished in that the nonrotating bearing parts which are the outer rings or races of the antifriction bearings, are supported relative to the stationary mounting support through an interposed rubber ring, which permits on the one hand a certain radial mobility of the driven shaft, and on the other has a function as a damping element, in that the rubber ring is squeezed in accordance with the deflection of the flexible bearing.
The friction unit is intended for an operation low in vibrations, and resonant vibrations are to be avoided.
This requirement is also met in the case of the friction unit which is known from DE OS 29 36 845. In this known friction unit, the friction element shafts are likewise supported with a radial play relative to the stationary mounting support in rubber rings, which exhibit damping properties.
These rubber rings are practice-proven, since they are reliable and wear-resistant, and moreover ensure a simple assembly of the friction false twist units.
When assembling the known friction false twist units, it is necessary to insert the rubber rings, together with the bearings, into the bores receiving the bearings in axial longitudinal direction of the shafts while radially compressing them.
However, the possibilities of installing the rubber rings are limited, since it is not possible to either compress them to any desired extent or insert them into the receiving bores in any desired oversize.
Accordingly, the very good damping properties of the known friction false twist units cannot be further improved without adversely affecting their assembly.
However, the development of these friction false twist units attempts to reach increasingly higher rotational speeds, so that vibrational problems arise therefrom in particular, when the friction element shafts pass through critical speeds.
In particular the passage through critical speeds requires with respect to the improved development of the friction false twist units an improved damping which is technically simple to realize.
In so doing, it should also be considered that the friction false twist units are equipped to an increasing extent with longer shafts and larger masses, so that a higher residual unbalance results which can practically not be balanced.
It is therefore the object of the present invention to further improve the known friction false twist unit such that its vibrational behavior is damped to a greater extent than before, and that yet its assembly is further simplified.
Radial deflections of the shaft are to remain small up to high rotational speeds (at least 20,000 rpm), in spite of the facts that a floating bearing is used, that the shafts are longer and equipped with larger masses than before, that the shafts and the friction disks arranged thereon cannot be prevented from having a residual unbalance, for example as a result of uneven wear, which can practically not be balanced, and that the shaft diameters are small. What matters in particular is that the axial position of the shaft relative to the housing should not change.